Molecular scissors

How do our cells attack foreign DNA?

Cells have a unique mechanism to protect themselves from attack
from viruses, fungi and bacteria. Inside each cell lies a group of
special proteins, called restriction enzymes.

Restriction enzymes cut the DNA of a foreign organism into
pieces before it has a chance to damage the cell. These enzymes are
just like scissors. They can chop up a piece of DNA into very small
pieces.

Restriction enzymes cut up
foreign DNA before it has chance to attack the cell

The blades of molecular scissors are not flat like regular
scissors. Instead they have 'teeth' that fit specific chemical
groups, called bases, on the DNA. Each blade has between 4-6
teeth.

A section of DNA can be made of several thousand bases. The
scissors will only cut a certain section of the DNA, when its teeth
are able to fit correctly between the bases. It's just like pieces
fitting together in a jigsaw. The section of DNA that the scissors
cut is called a 'recognition sequence' and is usually between 4-6
base pairs long.

Molecular scissors only cut a
specific piece of DNA

Host DNA (DNA from the animal or plant that is being attacked)
can also contain these recognition sequences.

In the host DNA, the bases making up the recognition sequence
are chemically modified. The restriction enzyme can no longer fit
correctly in between the bases. The host cell is protected from its
own restriction enzymes.

Why are restriction enzymes important?

Our cells are attacked by foreign microorganisms, like viruses,
every single day. If our cells didn't have restriction enzymes,
they would be unable to protect themselves. We would waste a lot of
our energy trying to recover from infections.

But that's not their only use. Molecular biologists have found a
way to use restriction enzymes.

The biologists use restriction enzymes to cut sections of DNA
from one organism and transfer it to another. This allows molecular
biologists to create hybrid DNA that has the best properties of
both organisms.

This technique has variety of uses in everyday medicine,
including producing insulin, antibiotics and fuel. Scientists have
also been using these enzymes to synthesise artificial DNA that can
power the growth and replication of a simple cell in the
laboratory.

One day this technology might help us make giant leaps in
medicine and green fuel production.

Are DNA restriction sequences the same for all animals? Find out
at Chop that
DNA!